Helium Plasma Research Articles

Investigation of small-fraction molecular impurities in high-pressure helium plasmas using optical plasma diagnostic methods

In high-pressure plasmas using gases diluted via a rare gas, small-fraction impurities in the discharge space significantly impact the basic plasma parameters and excited-species generation processes. This study investigated the behaviors of molecular impurities in a dielectric barrier discharge (DBD) generated in a flow of high-purity He gas using optical plasma diagnostic methods. The optical emission spectra obtained under various discharge conditions (pressure, flow rate, and voltage frequency) indicated that the major impurity species in the He DBD was the H2O molecule, and the DBD decomposed the H2O before reaching the measurement spot. To quantitatively analyze the H2O fraction, time-resolved laser absorption spectroscopy was performed to measure the exponential decay time of He metastable (Hem) atoms in the He-DBD. The H2O fraction in the He gas flow was derived from the dependence of Hem lifetime decay on the voltage frequency. In addition, a model was proposed to estimate the H2O fraction under various He pressure and flow rate conditions from reference data. The procedures to perform optical plasma diagnostics and evaluate the fraction and behavior of H2O impurities are expected to facilitate a better understanding and control of high-pressure plasmas.

Impact of helium and hydrogen plasma exposure on surface damage and erosion of tungsten

The impact of helium plasma exposure on the tungsten surface damage structure development and erosion has been investigated by comparing the impact of hydrogen plasma exposure. Crystal orientation dependence of the undulating surface structure formation and erosion rate is observed on the plasma-exposed tungsten surface independently from the plasma species. The top surface of the plasma exposed tungsten has a tendency to {100} plane independently from the initial surface orientation. Although hydrogen and/or helium cause no erosion in tungsten under incident ion energy exposure conditions below the sputtering threshold, inevitable minute impurities, like oxygen, play an essential role in erosion, and significant erosion can be observed even at 30 eV.

Evaluating the Healing Potential of J-Plasma Scalpel-Created Surgical Incisions in Porcine and Rat Models.

Cold atmospheric plasma devices generate reactive oxygen and nitrogen species that can be anti-microbial but also promote cell migration, differentiation, and tissue wound healing. This report investigates the healing of surgical incisions created using cold plasma generated by the J-Plasma scalpel (Precise Open handpiece, Apyx Medical, Inc.) compared to a steel scalpel in in vivo porcine and rat models. The J-Plasma scalpel is currently FDA approved for the delivery of helium plasma to cut, coagulate, and ablate soft tissue during surgical procedures. To our knowledge, this device has not been studied in creating surgical incisions but only during deeper dissection and hemostasis. External macroscopic and histologic grading by blinded reviewers revealed no significant difference in wound healing appearance or physiology in incisions created using the plasma scalpel as compared with a steel blade scalpel. Incisions created with the plasma scalpel also had superior hemostasis and a reduction in tissue and blood carryover. Scanning electron microscopy (SEM) and histology showed collagen fibril fusion occurred as the plasma scalpel incised through the tissue, contributing to a sealing effect. In addition, when bacteria were injected into the dermis before incision, the plasma scalpel disrupted the bacterial membrane as visualized in SEM images. External macroscopic and histologic grading by blinded reviewers revealed no significant difference in wound healing appearance or physiology. Based on these results, we propose additional studies to clinically evaluate the use of cold plasma in applications requiring hemostasis or when an increased likelihood of subdermal pathogen leakage could cause surgical site infection (i.e., sites with increased hair follicles).

Low onset potential for oxygen evolution reaction on hematite electrodes processed with He plasma irradiation

In this study, we investigated the effects of helium (He) plasma irradiation and thermal treatment on the morphology, the surface characteristics, and the photoelectrochemical performance of bulk iron (Fe) sheets. After processing, all samples consisted mainly of an α-Fe2O3 surface. Helium plasma irradiation resulted in a cathodic shift in the onset potential of the photocurrent from 1.16 VRHE (no pretreatment) to 0.57 VRHE (plasma exposure at 660 °C), where VRHE represents the potential versus reversible hydrogen electrode (RHE). An increase in the surface roughness and a smaller amount of hydroxyl or oxygen vacancies at the surface after photoelectrochemical measurement are related to the decrease of the onset potential. The results show that He plasma irradiation does not only modify the surface morphology, but also affects the functional properties of the materials.

Changeover between helium and hydrogen fueled plasmas in JET and WEST

The pre-fusion power operation (PFPO) phase of ITER, as described in the ITER research plan with Staged Approach,22ITER Organization, “ITER Research Plan within the Staged Approach,” ITR-18–003, Aug. 2018. includes both hydrogen (H) and helium (He) plasma operations. In preparation for PFPO, both WEST and JET ran He plasma campaigns to study plasma-wall interactions in a tungsten environment. The campaigns included a back-and-forth transition between H or deuterium (D) and He plasma operation allowing the assessment of the achievable plasma content as well as the accessible wall reservoirs for respective species. The WEST changeovers included tokamak pulses with a fixed divertor configuration. The JET changeovers applied ion cyclotron wall conditioning (ICWC) and tokamak pulses including limiter phases and four different divertor configurations. Glow discharge conditioning (GDC) was applied to complete the changeovers. The results are characterized by subdivertor optical and mass spectrometric gas analyzers and spatially resolved optical emission spectroscopy. A He content of 96–97 % after H operations is achieved by tens of ICWC pulses (JET) and several dedicated diverted plasmas (WEST and JET), while a fivefold is estimated to be required for the back transition. Effective pumping of the wall released species is a key parameter for a fast changeover. Upon applying higher heating power, the relative content of the fueled plasma species decreases. The JET gas balance analysis indicates that He operation may increase H retention. WEST divertor spectroscopy indicates a larger He inventory near the inner divertor strike line. He GDC has a clear effect on the He recycling light at the WEST divertor while D GDC did not reduce the long lasting He content observed in D pulses after the JET He campaign.

Influence of pulsed flows of helium ions and helium plasma on austenitic chromomanganeous steel preliminary irradiated with deuterium

Influence of pulsed flows of helium ions and helium plasma on austenitic chromomanganeous steel preliminary irradiated with deuterium

Identification of Different Classes of VOCs Based on Optical Emission Spectra Using a Dielectric Barrier Helium Plasma Coupled with a Mini Spectrometer.

In this study, a micro helium dielectric barrier discharge (μHDBD) plasma device fabricated using 3D printing and molding techniques was coupled with a mini spectrometer to detect and identify different classes of volatile organic compounds (VOCs) using optical emission spectrometry (OES). We tested 11 VOCs belonging to three different classes (straight-chain alkanes, aromatics, and polar organic compounds). Our results clearly demonstrate that the optical emission spectra of different classes of VOCs show clear differences, and therefore, can be used for identification. Additionally, the emission spectra of VOCs with a similar structure (such as n-pentane, n-hexane, n-heptane, n-octane, and n-nonane) have similar optical emission spectrum shape. Acetone and ethanol also have similar emission wavelengths, but they show different line intensities for the same concentrations. We also found that the side-chain group of aromatics will also affect the emission spectra even though they have a similar structure (all have a benzene ring). Moreover, our μHDBD-OES system can also identify multiple compounds in VOC mixtures. Our work also demonstrates the possibility of identifying different classes of VOCs by the OES shape.

Influence of Microsecond Pulse Helium Plasma Flow on the Surface Morphology and Crystal Structure of the Photovoltaic Converters Based on CdS/CdTe

Influence of Microsecond Pulse Helium Plasma Flow on the Surface Morphology and Crystal Structure of the Photovoltaic Converters Based on CdS/CdTe

Temporal evolution of the light emitted by a thin, laser-ionized plasma source

We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source. In addition, this work provides a detailed understanding of the plasma light measurement, which is one of the few diagnostic signals available for the direct measurement of PWFA plasma sources.

Effect of Helium Plasma Irradiation on Microstructures and Mechanical Properties of Tungsten

Effect of Helium Plasma Irradiation on Microstructures and Mechanical Properties of Tungsten

Effect of electron temperature and concentration on production of hydroxyl radical and nitric oxide in atmospheric pressure low-temperature helium plasma jet: Swarm analysis and global model investigation

Effect of electron temperature and concentration on production of hydroxyl radical and nitric oxide in atmospheric pressure low-temperature helium plasma jet: Swarm analysis and global model investigation

Effect of He diluted plasma on the deposition of flexible low-temperature polycrystalline silicon thin film

The growth of a low-temperature polycrystalline silicon (LTPS) thin film on a flexible polyethylene terephthalate (PET) substrate under the assistance of helium plasma has been examined in detail in this study. By utilizing the plasma enhanced chemical vapor deposition method, LTPS thin films are directly deposited on a PET substrate at a relatively low temperature (80 °C), and the variations in the morphology, structure, and electrical property of the samples with He flow are systematically characterized by performing a series of tests. The results show that the purely helium-diluted silane plasma has the function of inducing crystallization and fabricating the c-Si network. After optimizing the He flow rate to 600 SCCM, the LTPS thin film with the largest average grain size of ∼204.7 nm can be obtained, while the maximum dark conductivity (4.16 × 10−5 S/cm) is also achieved. Finally, a detailed discussion is presented to illustrate the growth mechanism of the LTPS thin film in He plasma.

Studies of the material erosion and deposition during the wall conditioning processes using quartz crystal microbalance in EAST

To study material erosion and deposition during different wall conditioning processes in the Experimental Advanced Superconducting Tokamak (EAST), two newly developed quartz crystal microbalances (QMBs) at the mid-plane of port C (C-QMB) and port J (J-QMB) with the same radial radius were used for in-situ and real-time measurements during the 2021 autumn experimental campaign. It was found that the material deposition was mainly influenced by the location of the antenna and the power of the ion cyclotron range of frequency (ICRF), rather than the location of the gas inlet, during the wall cleaning with helium plasma and siliconization assisted with ICRF plasma. The higher energy and density of plasma could result in higher deposition rates near the antenna. While, during lithium (Li) coating, the material deposition was greatly influenced by the location of the Li oven due to the deposition of unionized Li atoms. The ICRF power influenced the material deposition behavior far away from the Li ovens. Besides, a stronger effect on impurity suppression was observed with a more uniform deposition trend of Li coating. This necessitates further study on the influence of factors such as the location of the Li oven and ICRF antenna, the temperature of ovens, and ICRF power on the homogeneity of wall conditioning.

Formation of corrugated nano-fuzz tungsten thin film on silicon via helium plasma irradiation

Tungsten thin films were deposited onto silicon substrates using sputtering techniques, and helium plasma irradiation was performed in a linear plasma device. Observations of the surface and cross-sectional morphology revealed the presence of a corrugated fiberform nanostructure, referred to as corrugated nano-fuzz, on the irradiated silicon samples. This structure has a distinct pattern of ridges and valleys with nanofibers on the surface. In addition to its unique morphology, the corrugated nano-fuzz demonstrates remarkable optical absorptivity, as revealed by optical absorptivity measurements, even after being exposed to helium plasma even for a short duration. The utilization of silicon-substrate thin film holds the potential to not only accelerate the processing for nanostructure growth but also yield uniformly corrugated structures and high optical absorptivity. These findings offer valuable insights for advancing the development of efficient fabrication methods within the field of nanotechnology.

Plasma-Driven Synthesis of 3D Self-Supported Ni-Fe Nanostructures for Green Hydrogen Production

Hydrogen is considered as a future energy carrier due to its desirable characteristics such as high energy density, wide range of applications, and near-zero greenhouse gas emissions. Amongst the various hydrogen production methods, electrochemical water splitting is a promising alternative for producing large-scale green hydrogen. Recently, Anion Exchange Membrane Water Electrolysis (AEMWE) has garnered special attention due to its advantages such as use of low-cost materials and higher performance over conventional techniques such as Alkaline Water Electrolysis (AWE) or Proton Exchange Membrane Water Electrolysis (PEMWE).In the development of anodic electrodes for AEMWE, nickel-based materials have been extensively studied as promising low-cost substitutes to expensive noble metal catalysts such as IrO2 and RuO2. To improve the catalytic performance, interfacial engineering, intercalation, nanostructuring techniques are commonly used1. The nanostructured catalysts are typically synthesized in powder form, which then requires a binder to coat them on a substrate. The extra interfaces between the catalyst, substrate and the electrolyte can cause charge and mass transfer limitations as well as restrict the availability of active sites2. Under gas evolution conditions, it can also lead to mechanical shedding and delamination of catalysts. This limits the applicability of emerging electrocatalysts on a commercial scale, thus making it essential to explore novel fabrication routes for synthesizing self-supported nanostructures.Helium plasma irradiation is a potential alternative wherein the nanostructures are created on the substrate itself, and thus can potentially alleviate some of the shortcomings of conventional methods. The plasma irradiation technique has been extensively studied in relation to the surface erosion and embrittlement of fusion reactors3,4. However, its application has been limited mostly to planar surfaces and only a few studies have employed this technique in solar-to-hydrogen production5,6. Herein, we report plasma-driven synthesis of nanostructured 3D electrodes and their integration in a membrane electrode assembly (MEA).The MEA with self-supported nanostructures delivers ≈25% higher performance than its bare counterpart at room temperature. Additionally, iron incorporation further increases the performance, surpassing commercially available NiFe electrocatalysts. Going forward, the durability and performance of the self-supported electrodes at higher temperatures will be explored and the applicability of this technique to other renewable energy systems is expected to be correlated.

The Safety of Contraction of Subcutaneous Tissue Following Liposuction Procedures.

Abstract This paper examines the practice of using a helium plasma radiofrequency (RF) device for contracting subcutaneous soft tissue following liposuction in all body areas. A review of the data from 6 industry-sponsor-initiated retrospective studies was performed, wherein 483 real-world patients underwent liposuction followed by contraction of the subcutaneous soft tissue with the helium plasma RF system. These data were evaluated to determine if any new or increased risks were introduced compared to the risks of liposuction alone. The totality of the real-world data demonstrates there are no new or increased risks for helium plasma RF procedures following liposuction compared to liposuction alone. These data support the safety of helium plasma RF for subcutaneous soft-tissue contraction following liposuction. There are currently no alternative therapies specifically cleared by the FDA that can claim use following liposuction for the purpose of contracting the subcutaneous soft tissue. Level of Evidence: 3

Experimental scalings of scrape-off layer particle flux width by outboard divertor Langmuir probes for deuterium and helium plasmas on EAST

The scrape-off layer (SOL) power width (λq ) is an important parameter for predicting the heat load on divertor targets for future magnetically confined devices. Currently, the underlying physics for λq scaling is not fully understood. This paper extends the previous SOL particle flux width (λjs, λq ≈ λjs is assumed, js is the measured ion current density used as a proxy for particle flux) scaling measured by the inboard divertor Langmuir probes (Div-LPs) in deuterium plasmas (Liu et al 2019 Plasma Phys. Control. Fusion 61 045001) to the λjs scalings measured by the outboard Div-LPs in both deuterium and helium plasmas on EAST. A systematic method has been used to correct the upper-outer Div-LP measurements to reduce the measurement uncertainty of λjs . About 520 discharges are selected for the construction of six databases (H-mode, L-mode, and Ohmic for deuterium and helium plasmas) to scale λjs . Since the published λq scalings do not fit EAST λjs well in the databases, four separate λjs scalings are proposed using statistical method to minimize the scaling parameters. It is found that λjs has a robust scaling dependence on the plasma line-averaged density ( nˉe ) for both deuterium and helium plasmas and a strong positive scaling dependence on the divertor leg length (L div,leg). The scaling exponent of the stored energy agrees well with the previous λq /λjs scalings for deuterium plasmas. The near unity scaling exponents of edge safety factor and L div,leg reveal the importance of parallel connection length in determining λjs . The positive scaling dependence of λjs on nˉe and the 2 ∼ 4 times larger scaling amplitude compared with the published λq scalings probably indicate the turbulence broadening of λjs on EAST. The comparison of λjs for deuterium and helium plasmas using the constructed databases shows no significant difference. Statistical comparison of the normalized λjs with different ELM types suggests that the grassy-ELM λjs is slightly larger than the inter large-ELM (type-I ELM) λjs for both deuterium and helium plasmas.

Experimental Study of the Compressibility of a Helium Plasma at a Pressure up to 20 TPa

A nonideal helium plasma has been compressed to a density of ρ ≈ 14 g/cm3at a pressure ofP≈20TPa (200Mbar) in a spherical two-cascade device. The design of the device has been presented and the thermodynamic parameters of the helium plasma reached in it have been estimated. Data on the dynamics of the external and internal cascades in the device used to choose the calculation method have been obtained in a preliminary experiment with a hemispherical prototype. The experiment has been performed on the X-ray complex at the Russian Federal Nuclear Center All-Russian Research Institute of Experimental Physics, which includes BIM 234.3000 betatrons with a boundary energy of 60 MeV used in the multipulse bremsstrahlung generation regime with a multichannel optoelectronic system of recording X-ray images. A high-current linear accelerator LIU-R-T and an image detector assembly consisting of photochromic ADC screens have been used in addition to betatrons to detect the compressed shell cavity.

Broadening of He 1083nm, 388.8 nm, 501.6 nm, 587.5 nm, 667.8 nm, 706.5 nm, 728.1 nm lines and of H(α), H(β) and O 777 nm lines in atmospheric pressure helium

Helium atoms in electronically excited states are produced in atmospheric pressure parallel plate DBD helium plasma. Pressure broadening coefficients of several helium lines and of O(777 nm), H(β) and H(α) lines are deduced from the analysis of the spectral profiles of those lines. Absorption spectroscopy on He(3S) metastable atoms with a diode laser is used for 1083 nm He line. The influence of the laser power density on recorded absorption spectral profile is analyzed. For the other lines, emission from the plasma is analyzed with a very high resolution 2 m focal length spectrometer, working in the 2nd, 3rd or 4th diffraction order of the 1200 g/mm grating. Instrumental width ΔI ranges between 2.2 and 9.8 pm, depending on the spectral line. Knowing with high precision ΔI and the Doppler widths of the lines and the fact that the resulting Gaussian width of each line remains, at least, 4 times smaller than its Lorentzian width, permits to deduce the pressure broadening coefficients of helium 388.8, 501.6, 587.5, 667.8, 706.5, 728.1 and 1083 nm lines and of 777 O line with less than 3 % uncertainty for most of them. Observation of the forbidden 2p 1P1 –4f 1F3 component in the blue wing of the allowed 492.19 nm He(2p 1P1 –4d 1D2) line, indicates the presence of a static electric field E ≈ 5 ± 1 kV/cm during the 0.4 µs light collection time from the DBD. It is concluded that in pulsed plasmas, like DBD and plasma-jet, before deducing the plasma density from the homogeneous widths of H(β) or H(α) lines, one should ascertain that the static E-field in the gas is small enough during the light collection period for not inducing significant splitting of these lines. This would induce an extra broadening of the line, leading to an overestimated electron density.

Enhancing wettability and adhesive properties of PVDF-based substrates through non-thermal helium plasma surface modification

Polyvinylidene fluoride (PVDF) has gained attention as a promising material for tissue engineering due to its biocompatibility and piezoelectricity. However, achieving proper cell adhesion to PVDF surfaces remains a challenge. This study focuses on the preparation and characterization of PVDF-based substrates, including PVDF thin films and nanocomposites incorporating CoFe2O4 magnetic nanoparticles. Helium plasma treatment is employed to modify the surface properties of these substrates. The plasma treatment induces significant changes in the topography of the PVDF-based nanocomposites. The roughness values of the samples increase from 2–3 nm to 14–17 nm after 90 s of plasma treatment, leading to enhanced hydrophilicity with an average contact angle below 60°. Importantly, the helium plasma treatment preserves the magnetic and structural properties of the substrates, suggesting the retention of their magnetoelectric properties and, thus treated composites hold potential for remote stem cell activation. We provide evidence of cytocompatibility and improved adhesive properties of plasma-treated substrates using human mesenchymal stem cell cultures.